Thermosetting compositions containing carboxylic acid functional polymers prepared by atom transfer radical polymerization

ABSTRACT

A thermosetting composition comprising a co-reactable solid, particulate mixture of (a) polycarboxylic acid functional polymer, and (b) epoxide functional crosslinking agent having at least two epoxide groups, e.g., triglycidyl isocyanurate (TGIC), is described. The polycarboxylic acid functional polymer is prepared by atom transfer radical polymerization and has well defined polymer chain architecture and polydispersity index of less than 2.0. The thermosetting compositions of the present invention have utility as powder coatings compositions.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 60/098603, filed Aug. 31, 1998, which is hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to thermosetting compositions of one ormore carboxylic acid functional polymers and an epoxide functionalcrosslinking agent, such as tris(2,3-epoxypropyl) isocyanurate. Thecarboxylic acid functional polymer is prepared by atom transfer radicalpolymerization, and has well defined polymer chain structure, molecularweight and molecular weight distribution. The present invention alsorelates to methods of coating a substrate, and substrates coated by suchmethods.

BACKGROUND OF THE INVENTION

Reducing the environmental impact of coatings compositions, inparticular that associated with emissions into the air of volatileorganics during their use, has been an area of ongoing investigation anddevelopment in recent years. Accordingly, interest in powder coatingshas been increasing due, in part, to their inherently low volatileorganic content (VOC), which significantly reduces air emissions duringthe application process. While both thermoplastic and thermoset powdercoatings compositions are commercially available, thermoset powdercoatings are typically more desirable because of their superior physicalproperties, e.g., hardness and solvent resistance.

Low VOC coatings are particularly desirable in a number of applications,e.g., the automotive original equipment manufacture (OEM), industrialand appliance markets, due to the relatively large volume of coatingsthat are used. However, in addition to the requirement of low VOClevels, many manufacturers have strict performance requirements of thecoatings that are used. Examples of such requirements include, goodexterior durability, solvent resistance, and excellent gloss andappearance. While liquid topcoats can provide such properties, they havethe undesirable drawback of higher VOC levels relative to powdercoatings, which have essentially zero VOC levels.

Powder coatings based on carboxylic acid functional polymers cured withepoxide functional crosslinkers, such as tris(2,3-epoxypropyl)isocyanurate, (“epoxy cured powder coatings”) are known and have beendeveloped for use in a number of applications, such as industrial andautomotive OEM topcoats. The epoxide functional crosslinkertris(2,3-epoxypropyl) isocyanurate is also commonly referred to astriglycidyl isocyanurate (TGIC). Such epoxy cured powder coatings, inwhich the crosslinking agent is TGIC, are described in, for example,U.S. Pat. Nos. 3,935,138, 4,242,253, 4,605,710, 4,910,287, 5,264,529 and5,684,067. However, their use has been limited due to deficiencies in,for example, flow, appearance and storage stability. The binder of epoxycured powder coatings compositions typically comprises polyester and/oracrylic polymers having carboxylic acid functionality. The carboxylicacid functional polymers used in such epoxy cured powder coatingscompositions are typically prepared by standard, i.e., non-living,radical polymerization methods, which provide little control overmolecular weight, molecular weight distribution and polymer chainstructure.

The physical properties, e.g., glass transition temperature (Tg) andmelt viscosity, of a given polymer can be directly related to itsmolecular weight. Higher molecular weights are typically associatedwith, for example, higher Tg values and melt viscosities. The physicalproperties of a polymer having a broad molecular weight distribution,e.g., having a polydispersity index (PDI) in excess of 2.0 or 2.5, canbe characterized as an average of the individual physical properties ofand indeterminate interactions between the various polymeric speciesthat comprise it. As such, the physical properties of polymers havingbroad molecular weight distributions can be variable and hard tocontrol.

The polymer chain structure, or architecture, of a copolymer can bedescribed as the sequence of monomer residues along the polymer backboneor chain. For example, a carboxylic acid functional copolymer preparedby standard radical polymerization techniques will contain a mixture ofpolymer molecules having varying individual carboxylic acid equivalentweights. Some of these polymer molecules can actually be free ofcarboxylic acid functionality. In a thermosetting composition, theformation of a three dimensional crosslinked network is dependent uponthe functional equivalent weight as well as the architecture of theindividual polymer molecules that comprise it. Polymer molecules havinglittle or no reactive functionality (or having functional groups thatare unlikely to participate in crosslinking reactions due to theirlocation along the polymer chain) will contribute little or nothing tothe formation of the three dimensional crosslink network, resulting inless than desirable physical properties of the finally formedpolymerizate, e.g., a cured or thermoset coating.

The continued development of new and improved epoxy cured powdercoatings compositions having essentially zero VOC levels and acombination of favorable performance properties is desirable. Inparticular, it would be desirable to develop epoxy cured powder coatingscompositions that comprise carboxylic acid functional polymers havingwell defined molecular weights and polymer chain structure, and narrowmolecular weight distributions, e.g., PDI values less than 2.5.Controlling the architecture and polydispersity of the carboxylic acidfunctional polymer is desirable in that it enables one to achieve higherTg's and lower melt viscosities than comparable carboxylic acidfunctional polymers prepared by conventional processes, resulting inthermosetting particulate compositions which are resistant to caking andhave improved physical properties.

International patent publication WO 97/18247 and U.S. Pat. Nos.5,763,548 and 5,789,487 describe a radical polymerization processreferred to as atom transfer radical polymerization (ATRP). The ATRPprocess is described as being a living radical polymerization thatresults in the formation of (co)polymers having predictable molecularweight and molecular weight distribution. The ATRP process is alsodescribed as providing highly uniform products having controlledstructure (i.e., controllable topology, composition, etc.). The '548 and'487 patents and WO 97/18247 patent publication also describe(co)polymers prepared by ATRP, which are useful in a wide variety ofapplications, for example, with paints and coatings.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided, athermosetting composition comprising a co-reactable solid, particulatemixture of:

(a) polycarboxylic acid functional polymer prepared by atom transferradical polymerization initiated in the presence of an initiator havingat least one radically transferable group, and in which said polymercontains at least one of the following polymer chain structures I andII:

—[(M)_(p)—(G)_(q)]_(x)—  I

and

—[(G)_(q)—(M)_(p)]_(x)—  II

wherein M is a residue, that is free of carboxylic acid functionality,of at least one ethylenically unsaturated radically polymerizablemonomer; G is a residue, that has carboxylic acid functionality, of atleast one ethylenically unsaturated radically polymerizable monomer; pand q represent average numbers of residues occurring in a block ofresidues in each polymer chain structure; and p, q and x are eachindividually selected for each structure such that said polycarboxylicacid functional polymer has a number average molecular weight of atleast 250; and

(b) epoxide functional crosslinking agent having at least two epoxidegroups.

In accordance with the present invention, there is also provided amethod of coating a substrate with the above described thermosettingcomposition.

There is further provided, in accordance with the present invention, amulti-component composite coating composition comprising a base coatdeposited from a pigmented film-forming composition, and a transparenttop coat applied over the base coat. The transparent top coat comprisesthe above described thermosetting composition

Other than in the operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients, reaction conditions, andso forth used in the specification and claims are to be understood asmodified in all instances by the term “about.”

As used herein, the term “polymer” is meant to refer to bothhomopolymers, i.e., polymers made from a single monomer species, andcopolymers, i.e., polymers made from two or more monomer species.

DETAILED DESCRIPTION OF THE INVENTION

Thermosetting compositions in accordance with the present invention,comprise one or more polycarboxylic acid functional polymers. As usedherein and in the claims, by “polycarboxylic acid functional polymer”and like terms is meant a polymer having two or more carboxylic acidgroups in terminal and/or pendent positions that are capable of reactingand forming covalent bonds with compounds containing epoxide (oroxirane) groups.

The carboxylic acid functional polymer of the present invention isprepared by atom transfer radical polymerization (ATRP). The ATRP methodis described as a “living polymerization,” i.e., a chain-growthpolymerization that propagates with essentially no chain transfer andessentially no chain termination. The molecular weight of a polymerprepared by ATRP can be controlled by the stoichiometry of thereactants, i.e., the initial concentration of monomer(s) andinitiator(s). In addition, ATRP also provides polymers havingcharacteristics including, for example, narrow molecular weightdistributions, e.g., PDI values less than 2.5, and well defined polymerchain structure, e.g., block copolymers and alternating copolymers.

The ATRP process can be described generally as comprising: polymerizingone or more radically polymerizable monomers in the presence of aninitiation system; forming a polymer; and isolating the formed polymer.The initiation system comprises: an initiator having a radicallytransferable atom or group; a transition metal compound, i.e., acatalyst, which participates in a reversible redox cycle with theinitiator; and a ligand, which coordinates with the transition metalcompound. The ATRP process is described in further detail ininternational patent publication WO 97/18247 and U.S. Pat. Nos.5,763,548 and 5,789,487.

In preparing carboxylic acid functional polymers of the presentinvention, the initiator may be selected from the group consisting oflinear or branched aliphatic compounds, cycloaliphatic compounds,aromatic compounds, polycyclic aromatic compounds, heterocycliccompounds, sulfonyl compounds, sulfenyl compounds, esters of carboxylicacids, polymeric compounds and mixtures thereof, each having at leastone radically transferable group, which is typically a halo group. Theinitiator may also be substituted with functional groups, e.g., oxyranylgroups, such as glycidyl groups. Additional useful initiators and thevarious radically transferable groups that may be associated with themare described on pages 42 through 45 of international patent publicationWO 97/18247.

Polymeric compounds (including oligomeric compounds) having radicallytransferable groups may be used as initiators, and are herein referredto as “macroinitiators.” Examples of macroinitiators include, but arenot limited to, polystyrene prepared by cationic polymerization andhaving a terminal halide, e.g., chloride, and a polymer of2-(2-bromopropionoxy) ethyl acrylate and one or more alkyl(meth)acrylates, e.g., butyl acrylate, prepared by conventionalnon-living radical polymerization. Macroinitiators can be used in theATRP process to prepare graft polymers, such as grafted block copolymersand comb copolymers. A further discussion of macroinitiators is found onpages 31 through 38 of international patent publication WO 98/01480.

Preferably, the initiator may be selected from the group consisting ofhalomethane, methylenedihalide, haloform, carbon tetrahalide,1-halo-2,3-epoxypropane, methanesulfonyl halide, p-tolue~nesulfonylhalide, methanesulfenyl halide, p-toluenezsulfenyl halide, 1-phenylethylhalide, C₁-C₆-alkyl ester of 2-halo-C₁-C₆-carboxylic acid,p-halomethylstyrene, mono-hexakis (α-halo-C₁-C₆-alkyl)benzene,diethyl-2-halo-2-methyl malonate, ethyl 2-bromoisobutyrate and mixturesthereof. A particularly preferred initiator is diethyl-2-bromo-2-methylmalonate.

Catalysts that may be used in preparing carboxylic acid functionalpolymers of the present invention, include any transition metal compoundthat can participate in a redox cycle with the initiator and the growingpolymer chain. It is preferred that the transition metal compound notform direct carbon-metal bonds with the polymer chain. Transition metalcatalysts useful in the present invention may be represented by thefollowing general formula III,

TM ^(n+) X _(n)  III

wherein TM is the transition metal, n is the formal charge on thetransition metal having a value of from 0 to 7, and X is a counterion orcovalently bonded component. Examples of the transition metal (TM)include, but are not limited to, Cu, Fe, Au, Ag, Hg, Pd, Pt, Co, Mn, Ru,Mo, Nb and Zn. Examples of X include, but are not limited to, halogen,hydroxy, oxygen, C₁-C₆-aloxy, cyano, cyanato, thiocyanato and azido. Apreferred transition metal is Cu(I) and X is preferably halogen, e.g.,chloride. Accordingly, a preferred class of transition metal catalystsare the copper halides, e.g., Cu(I)Cl. It is also preferred that thetransition metal catalyst contain a small amount, e.g., 1 mole percent,of a redox conjugate, for example, Cu(II)Cl₂ when Cu(I)Cl is used.Additional catalysts useful in preparing the carboxylic acid functionalpolymers of the present invention are described on pages 45 and 46 ofinternational patent publication WO 97/18247. Redox conjugates aredescribed on pages 27 through 33 of international patent publication WO97/18247.

Ligands that may be used in preparing carboxylic acid functionalpolymers of the present invention, include, but are not limited tocompounds having one or more nitrogen, oxygen, phosphorus and/or sulfuratoms, which can coordinate to the transition metal catalyst compound,e.g., through sigma and/or pi bonds. Classes of useful ligands, includebut are not limited to: unsubstituted and substituted pyridines andbipyridines; porphyrins; cryptands; crown ethers; e.g., 18-crown-6;polyamines, e.g., ethylenediamine; glycols, e.g., alkylene glycols, suchas ethylene glycol; carbon monoxide; and coordinating monomers, e.g.,styrene, acrylonitrile and hydroxyalkyl (meth)acrylates. A preferredclass of ligands are the substituted bipyridines, e.g.,4,4′-dialkylbipyridyls. Additional ligands that may be used in preparingthe carboxylic acid functional polymers of the present invention aredescribed on pages 46 through 53 of international patent publication WO97/18247.

In preparing the carboxylic acid functional polymers of the presentinvention the amounts and relative proportions of initiator, transitionmetal compound and ligand are those for which ATRP is most effectivelyperformed. The amount of initiator used can vary widely and is typicallypresent in the reaction medium in a concentration of from 10⁻⁴moles/liter (M) to 3 M, for example, from 10⁻³ M to 10⁻¹ M. As themolecular weight of the carboxylic acid functional polymer can bedirectly related to the relative concentrations of initiator andmonomer(s), the molar ratio of initiator to monomer is an importantfactor in polymer preparation. The molar ratio of initiator to monomeris typically within the range of 10⁻⁴:1 to 0.5:1, for example, 10⁻³:1 to5×10⁻²:1.

In preparing the carboxylic acid functional polymers of the presentinvention, the molar ratio of transition metal compound to initiator istypically in the range of 10⁻⁴:1 to 10:1, for example, 0.1:1 to 5:1. Themolar ratio of ligand to transition metal compound is typically withinthe range of 0.1:1 to 100:1, for example, 0.2:1 to 10:1.

Carboxylic acid functional polymers useful in the thermosettingcompositions of the present invention may be prepared in the absence ofsolvent, i.e., by means of a bulk polymerization process. Generally, thecarboxylic acid functional polymer is prepared in the presence of asolvent, typically water and/or an organic solvent. Classes of usefulorganic solvents include, but are not limited to, esters of carboxylicacids, ethers, cyclic ethers, C₅-C₁₀ alkanes, C₅-C₈ cycloalkanes,aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, amides,nitrites, sulfoxides, sulfones and mixtures thereof. Supercriticalsolvents, such as CO₂, C₁-C₄ alkanes and fluorocarbons, may also beemployed. A preferred class of solvents are the aromatic hydrocarbonsolvents, particularly preferred examples of which are xylene, and mixedaromatic solvents such as those commercially available from ExxonChemical America under the trademark SOLVESSO. Additional solvents aredescribed in further detail on pages 53 through 56 of internationalpatent publication WO 97/18247.

Due to the possible deactivation of some ATRP catalysts, e.g., copper,in the presence of carboxylic acid groups, the above described ATRPprocess is generally performed in the substantial absence of carboxylicacid functionality. Accordingly, the carboxylic acid functional polymerused in the composition of the present invention is typically preparedin two stages. The first stage involves the ATRP preparation of aprecursor of the polycarboxylic acid functional polymer that issubstantially free of carboxylic acid functionality (“precursorpolymer”). In the second stage, the precursor polymer is converted tothe polycarboxylic acid functional polymer of the composition of thepresent invention.

The conversion of the precursor polymer to the polycarboxylic acidfunctional polymer is accomplished using methods known to those ofordinary skill in the art. Such known methods of conversion include, butare not limited to: (a) hydrolyzing residues of alkyl (meth)acrylatemonomers, e.g., t-butyl methacrylate, present in the backbone of theprecursor polymer; and (b) reacting residues of hydroxy functionalethylenically unsaturated radically polymerizable monomers present inthe backbone of the precursor polymer with cyclic anhydrides, e.g.,succinic anhydride.

The precursor polymer of the carboxylic acid functional polymer istypically prepared at a reaction temperature within the range of 25° C.to 140° C., e.g., from 50° C. to 100° C., and a pressure within therange of 1 to 100 atmospheres, usually at ambient pressure. The atomtransfer radical polymerization is typically completed in less than 24hours, e.g., between 1 and 8 hours.

When the carboxylic acid functional polymer is prepared in the presenceof a solvent, the solvent is removed after the polymer has been formed,by appropriate means as are known to those of ordinary skill in the art,e.g., vacuum distillation. Alternatively, the polymer may beprecipitated out of the solvent, filtered, washed and dried according toknown methods. After removal of, or separation from, the solvent, thecarboxylic acid functional polymer typically has a solids (as measuredby placing a 1 gram sample in a 110° C. oven for 60 minutes) of at least95 percent, and preferably at least 98 percent, by weight based on totalpolymer weight.

Prior to use in the thermosetting compositions of the present invention,the ATRP transition metal catalyst and its associated ligand aretypically separated or removed from the carboxylic acid functionalpolymer. The ATRP catalyst is preferably removed prior to conversion ofthe precursor polymer to the carboxylic acid functional polymer. Removalof the ATRP catalyst is achieved using known methods, including, forexample, adding a catalyst binding agent to the a mixture of theprecursor polymer, solvent and catalyst, followed by filtering. Examplesof suitable catalyst binding agents include, for example, alumina,silica, clay or a combination thereof. A mixture of the precursorpolymer, solvent and ATRP catalyst may be passed through a bed ofcatalyst binding agent. Alternatively, the ATRP catalyst may be oxidizedin situ and retained in the precursor polymer.

The carboxylic acid functional polymer may be selected from the groupconsisting of linear polymers, branched polymers, hyperbranchedpolymers, star polymers, graft polymers and mixtures thereof. The form,or gross architecture, of the polymer can be controlled by the choice ofinitiator and monomers used in its preparation. Linear carboxylic acidfunctional polymers may be prepared by using initiators having one ortwo radically transferable groups, e.g., diethyl-2-halo-2-methylmalonate and α, α′-dichloroxylene. Branched carboxylic acid functionalpolymers may be prepared by using branching monomers, i.e., monomerscontaining radically transferable groups or more than one ethylenicallyunsaturated radically polymerizable group, e.g.,2-(2-bromopropionoxy)ethyl acrylate, p-chloromethylstyrene anddiethyleneglycol bis(methacrylate). Hyperbranched carboxylic acidfunctional polymers may be prepared by increasing the amount ofbranching monomer used.

Star carboxylic acid functional polymers may be prepared usinginitiators having three or more radically transferable groups, e.g.,hexakis(bromomethyl)benzene. As is known to those of ordinary skill inthe art, star polymers may be prepared by core-arm or arm-core methods.In the core-arm method, the star polymer is prepared by polymerizingmonomers in the presence of the polyfunctional initiator, e.g.,hexakis(bromomethyl)benzene. Polymer chains, or arms, of similarcomposition and architecture grow out from the initiator core, in thecore-arm method.

In the arm-core method, the arms are prepared separately from the coreand optionally may have different compositions, architecture, molecularweight and PDI's. The arms may have different carboxylic acid equivalentweights, and some may have no carboxylic acid functionality. After thepreparation of the arms, they are attached to the core. For example, thearms may be prepared as precursor polymers by ATRP using glycidylfunctional initiators. These arms are then attached to a core havingthree or more active hydrogen groups that are reactive with epoxides,e.g., carboxylic acid or hydroxyl groups. Finally, the precursor polymerarms of the formed star polymer are converted to carboxylic acidfunctional arms, as discussed previously herein. The core can be amolecule, such as citric acid, or a core-arm star polymer prepared byATRP and having terminal reactive hydrogen containing groups, e.g.,carboxylic acid, thiol or hydroxyl groups.

An example of a core prepared by ATRP methods that can be used as a corein an ATRP arm-core star polymer is described as follows. In the firststage, 6 moles of methyl methacrylate are polymerized in the presence ofone mole of 1,3,5-tris(bromomethyl)benzene. In the second stage 3 molesof 2-hydroxyethyl methacrylate are fed to the reaction mixture. The corehaving terminal residues of 2-hydroxyethyl methacrylate is isolated andthen in the third stage reacted with a cyclic anhydride, such assuccinic anhydride. In the next stage, three precursor polymer arms ofvarying or equivalent composition and at least one of which has beenprepared by ATRP, are connected to the carboxylic acid terminated coreby reaction between the carboxylic acid groups of the core and reactivefunctionality in the arms, e.g., epoxide groups. The attached precursorpolymer arms of the star polymer are then converted to carboxylic acidfunctional arms.

Carboxylic acid functional polymers in the form of graft polymers may beprepared using a macroinitiator, as previously described herein. Graft,branched, hyperbranched and star polymers are described in furtherdetail on pages 79 through 91 of international patent publication WO97/18247.

The polydispersity index (PDI) of carboxylic acid functional polymersuseful in the present invention, is typically less than 2.5, moretypically less than 2.0, and preferably less than 1.8, for example, 1.5.As used herein, and in the claims, “polydispersity index” is determinedfrom the following equation: (weight average molecular weight(Mw)/number average molecular weight (Mn)). A monodisperse polymer has aPDI of 1.0. Further, as used herein, Mn and Mw are determined from gelpermeation chromatography using polystyrene standards.

General polymer chain structures I and II together or separatelyrepresent one or more structures that comprise the polymer chain, orback bone, architecture of the carboxylic acid functional polymer.Subscripts p and q of general polymer chain structures I and IIrepresent average numbers of residues occurring in the M and G blocks ofresidues respectively. Subscript x represents the number of segments ofM and G blocks, i.e., x-segments. Subscripts p and q may each be thesame or different for each x-segment. The following are presented forthe purpose of illustrating the various polymer architectures that arerepresented by general polymer chain structures I and II.

Homoblock polymer Architecture

When x is 1, p is 0 and q is 5, general polymer chain structure Irepresents a homoblock of 5 G residues, as more specifically depicted bythe following general formula IV.

—(G)—(G)—(G)—(G)—(G)—  IV

Diblock Copolymer Architecture

When x is 1, p is 5 and q is 5, general polymer chain structure Irepresents a diblock of 5 M residues and 5 G residues as morespecifically depicted by the following general formula V.

—(M)—(M)—(M)—(M)—(M)—(G)—(G)—(G)—(G)—(G)—  V

Alternating Copolymer Architecture

When x is greater than 1, for example, 5, and p and q are each for eachx-segment, polymer chain structure I represents an alternating block ofM and G residues, as more specifically depicted by the following generalformula VI.

—(M)—(G)—(M)—(G)—(M)—(G)—(M)—(G)—(M)—(G)—  VI

Gradient Copolymer Architecture

When x is greater than 1, for example, 3, and p and q are eachindependently within the range of, for example, 1 to 3, for eachx-segment, polymer chain structure I represents a gradient block of Mand G residues, as more specifically depicted by the following generalformula VII.

—(M)—(M)—(M)—(G)—(M)—(M)—(G)—(G)—(M)—(G)—(G)—(G)—  VII

Gradient copolymers can be prepared from two or more monomers by ATRPmethods, and are generally described as having architecture that changesgradually and in a systematic and predictable manner along the polymerbackbone. Gradient copolymers can be prepared by ATRP methods by (a)varying the ratio of monomers fed to the reaction medium during thecourse of the polymerization, (b) using a monomer feed containingmonomers having different rates of polymerization, or (c) a combinationof (a) and (b). Gradient copolymers are described in further detail onpages 72 through 78 of international patent publication WO 97/18247.

With further reference to general polymer chain structures I and II, Mrepresents one or more types of residues that are free of carboxylicacid functionality, and p represents the average total number of Mresidues occurring per block of M residues (M-block) within anx-segment. The —(M)_(p)— portion of general structures I and IIrepresents (1) a homoblock of a single type of M residue, (2) analternating block of two types of M residues, (3) a polyblock of two ormore types of M residues, or (4) a gradient block of two or more typesof M residues.

For purposes of illustration, when the M-block is prepared from, forexample, 10 moles of methyl methacrylate, the —(M)_(p)— portion ofstructures I and II represents a homohhock of 10 residues of methylmethacrylate. In the case where the M-block is prepared from, forexample, 5 moles of mehyl methacrylate and 5 moles of butylmethacrylate, the —(M)_(p)— portion of general structures I and IIrepresents, depending on the conditions of preparation, as is known toone of ordinary skill in the art: (a) a diblock of 5 residues of methylmethacrylate and 5 residues of butyl methacrylate having a total of 10residues (i.e., p=10); (b) a diblock of 5 residues of butyl methacrylateand 5 residues of methyl methacrylate having a total of 10 residues; (c)an alternating block of methyl methacrylate and butyl methacrylateresidues beginning with either a residue of methyl methacrylate or aresidue of butyl methacrylate, and having a total of 10 residues; or (d)a gradient block of methyl methacrylate and butyl methacrylate residuesbeginning with either residues of methyl methacrylate or residues ofbutyl methacrylate having a total of 10 residues.

Also, with reference to general polymer chain structures I and II, Grepresents one or more types of residues that have carboxylic acidfunctionality, and q represents the average total number of G residuesoccurring per block of G residues (G-block). Accordingly, the —(G)_(q)—portions of polymer chain structures I and II may be described in amanner similar to that of the —(M)_(p)— portions provided above.

Residue M of general polymer chain structures I and II is derived fromat least one ethylenically unsaturated radically polymerizable monomer.As used herein and in the claims, “ethylenically unsaturated radicallypolymerizable monomer” and like terms are meant to include vinylmonomers, allylic monomers, olefins and other ethylenically unsaturatedmonomers that are radically polymerizable.

Classes of vinyl monomers from which M may be derived include, but arenot limited to, (methh)acrylates, vinyl aromatic monomers, vinyl halidesand vinyl esters of carboxylic acids. As used herein and in the claims,by “(meth)acrylate” and like terms is meant both methacrylates andacrylates. Preferably, residue M is derived from at least one of alkyl(meth)acrylates having from 1 to 20 carbon atoms in the alkyl group.Specific examples of alkyl (meth)acrylates having from 1 to 20 carbonatoms in the alkyl group from which residue M may be derived include,but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate,propyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate,isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl(meth)acrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate,cyclohexyl (meth)acrylate and 3,3,5-trimethylcyclohexyl (meth)acrylate.

Residue M may also be selected from monomers having more than one(meth)acrylate group, for example, (meth)acrylic anhydride anddiethyleneglycol bis((meth)acrylate). Residue M may also be selectedfrom alkyl (meth)acrylates containing radically transferable groups,which can act as branching monomers, for example,2-(2-bromopropionoxy)ethyl acrylate.

Specific examples of vinyl aromatic monomers from which M may be derivedinclude, but are not limited to, styrene, p-chloromethylstyrene, divinylbenzene, vinyl naphthalene and divinyl naphthalene. Vinyl halides fromwhich M may be derived include, but are not limited to, vinyl chlorideand vinylidene fluoride. Vinyl esters of carboxylic acids from which Mmay be derived include, but are not limited to, vinyl acetate, vinylbutyrate, vinyl 3,4-dimethoxybenzoate and vinyl benzoate.

As used herein and in the claims, by “olefin” and like terms is meantunsaturated aliphatic hydrocarbons having one or more double bonds, suchas obtained by cracking petroleum fractions. Specific examples ofolefins from which M may be derived include, but are not limited to,propylene, 1-butene, 1,3-butadiene, isobutylene and diisobutylene.

As used herein and in the claims, by “allylic monomer(s)” is meantmonomers containing substituted and/or unsubstituted allylicfunctionality, i.e., one or more radicals represented by the followinggeneral formula VIII,

H₂C═C (R₄)—CH₂—  VIII

wherein R4 is hydrogen, halogen or a C₁ to C₄ alkyl group. Mostcommonly, R₄ is hydrogen or methyl and consequently general formula VIIIrepresents the unsubstituted (meth)allyl radical. Examples of allylicmonomers include, but are not limited to: (meth)allyl alcohol;(meth)allyl ethers, such as methyl (meth)allyl ether; allyl esters ofcarboxylic acids, such as (meth)allyl acetate, (meth)allyl butyrate,(meth)allyl 3,4-dimethoxybenzoate and (meth)allyl benzoate.

Other ethylenically unsaturated radically polymerizable monomers fromwhich M may be derived include, but are not limited to: cyclicanhydrides, e.g., maleic anhydride, 1-cyclopentene-1,2-dicarboxylicanhydride and itaconic anhydride; esters of acids that are unsaturatedbut do not have α, β-ethylenic unsaturation, e.g., methyl ester ofundecylenic acid; and diesters of ethylenically unsaturated dibasicacids, e.g., diethyl maleate.

Residue G of general polymer chain structures I and II is typicallyderived from: alkyl (meth)acrylate, which after polymerization ishydrolyzed; or at least one hydroxy functional ethylenically unsaturatedradically polymerizable monomer, which after polymerization ispost-reacted with a cyclic anhydride. Examples of classes of suitablehydroxy functional ethylenically unsaturated radically polymerizablemonomers from which residue G may be derived include, but are notlimited to: vinyl esters such as vinyl acetate, which are hydrolyzed toresidues of vinyl alcohol after polymerization; allylic esters such asallyl acetate, which are hydrolyzed to residues of allyl alcohol afterpolymerization; allylic functional monomer that also have hydroxyfunctionality, e.g., allyl alcohol and 2-allylphenol; vinyl aromaticmonomers having hydroxy functionality, e.g., 2-ethenyl-5-methyl phenol,2-ethenyl-6-methyl phenol and 4-ethenyl-3-methyl phenol; and hydroxyfunctional (meth)acrylates such as hydroxyalkyl (meth)acrylates, e.g.,hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate.

The cyclic anhydride is selected from those which can react withresidues of the hydroxy functional ethylenically unsaturated radicallypolymerizable monomers in the precursor polymer backbone, therebyattaching carboxylic acid groups thereto. Examples of suitable cyclicanhydrides include, but are not limited to, succinic anhydride, maleicanhydride, glutaric anhydride, adipic anhydride and pimelic anhydride.

In a preferred embodiment of the present invention, residue G is derivedfrom: C₁-C₄ alkyl (meth)acrylate, e.g., t-butyl methacrylate, whichafter polymerization is hydrolyzed; or at least one of hydroxyethyl(meth)acrylate and hydroxypropyl (meth)acrylate, which afterpolymerization is post-reacted with a cyclic anhydride, e.g., succinicanhydride.

Residue G may also be derived from other monomers which can be convertedor further reacted with other compounds to provide acid functionalityafter completion of the ATRP polymerization process. Examples of suchother monomers from which residue G may be derived include, but are notlimited to: acrylonitrile, the nitrile portion of which can behydrolyzed to a carboxylic acid group after polymerization; isocyanatefunctional monomers, e.g., 3-isopropenyl-α, α-dimethylbenzyl isocyanate[chemical abstracts (CAS) registry number 2094-99-7], which can bereacted after polymerization with compounds containing both carboxylicacid and hydroxyl functionality, e.g., 12-hydroxystearic acid and lacticacid; and maleic anhydride, which after polymerization can be eitherhydrolyzed to form carboxylic acid groups or reacted with amonofunctional alcohol in the presence of acid catalyst to form esterand carboxylic acid groups.

The choice of monomers from which each of residues M and G are selectedis interrelated, i.e., the choice of monomers from which G is derivedlimits the choice of monomers from which M is derived. When residue G isderived from hydroxy functional ethylenically unsaturated radicallypolymerizable monomer(s), which after polymerization are post-reactedwith a cyclic anhydride, residue M is typically not derived from suchmonomer(s). Also, when residue G is derived from one or more alkyl(meth)acrylates, which after polymerization are hydrolyzed, residue M istypically not derived from such monomers.

Subscripts p and q represent average number of residues occurring in ablock of residues in each polymer structure. Typically, p and q eachindependently have a value of 0 or more, preferably at least 1, and morepreferably at least 5 for each of general polymer structures I and II.Also, subscripts p and q each independently have a value of typicallyless than 100, preferably less than 20, and more preferably less than 15for each of general polymer structures I and II. The values ofsubscripts p and q may range between any combination of these values,inclusive of the recited values. Moreover, the sum of p and q is atleast 1 within an x-segment and q is at least 1 within at least onex-segment in the polymer.

Subscript x of general polymer structures I and II typically has a valueof at least 1. Also, subscript x typically has a value of less than 100,preferably less than 50, and more preferably less than 10. The value ofsubscript x may range between any combination of these values, inclusiveof the recited values. If more than one of the structures I and/or IIoccur in the polymer molecule, x may have different values for eachstructure (as may p and q), allowing for a variety of polymerarchitectures such as gradient copolymers.

The polycarboxylic acid functional polymer of the present invention maybe further described as having at least one of the following generalpolymer chain structures IX and X:

φ—[[(M)_(p)—(G)_(q)]_(x)—(M)_(r)—T]_(z)  IX

and

φ—[[(G)_(q)—(M)_(p)]_(x)—(G)_(s)—T]_(z)  X

wherein p, q, x, M and G have the same meanings as previously describedherein. The subscripts r and s represent average numbers of residuesoccurring in the respective blocks of M and G residues. The —(M)_(r)—and —(G)_(s)— portions of general formulas IX and X have meaningssimilar to those as previously described herein with regard to portions—(M)_(p)— and —(G)_(q)—

General polymer chain structures IX and X can represent the polymeritself or, alternatively, each of the structures can comprise a terminalsegment of the polymer. For example, where z is 1, the structures IX andX can represent a linear polymer, prepared by ATRP using an initiatorhaving 1 radically transferable group. Where z is 2, the structures IXand X can represent a linear “leg” extending from the residue of aninitiator having 2 radically transferable groups. Alternatively, where zis greater than 2, the structures IX and X can each represent an “arm”of a star polymer prepared by ATRP, using an initiator having more than2 radically transferable groups.

Symbol φ of general formulas IX and X is or is derived from the residueof the initiator used in the ATRP preparation of the polymer, and isfree of the radically transferable group of the initiator. For example,when the carboxylic acid functional polymer is initiated in the presenceof benzyl bromide, the symbol φ, more specifically φ-, is the benzyl

residue,

The symbol φ may also be derived from the residue of the initiator. Forexample, when the carboxylic acid functional polymer is initiated usingepichlorohydrin the symbol φ, more

specifically φ-, is the 2,3-epoxy-propyl residue, The 2,3-epoxy-propylresidue can then be converted to, for example, a 2,3-dihydroxypropylresidue.

In general formulas IX and X, subscript z is equal to the number ofcarboxylic acid functional polymer chains that are attached to φ.Subscript z is at least 1 and may have a wide range of values. In thecase of comb or graft polymers, wherein φ is a macroinitiator havingseveral pendent radically transferable groups, z can have a value inexcess of 10, for example 50, 100 or 1000. Typically, z is less than 10,preferably less than 6 and more preferably less than 5. In a preferredembodiment of the present invention, z is 1 or 2.

Symbol T of general formulas IX and X is or is derived from theradically transferable group of the initiator. For example, when thecarboxylic acid functional polymer is prepared in the presence ofdiethyl-2-bromo-2-methyl malonate, T may be the radically transferablebromo group.

The radically transferable group may optionally be (a) removed or (b)chemically converted to another moiety. In either of (a) or (b), thesymbol T is considered herein to be derived from the radicallytransferable group of the initiator. The radically transferable groupmay be removed by substitution with a nucleophilic compound, e.g., analkali metal alkoxylate. However, in the present invention, it isdesirable that the method by which the radically transferable group iseither removed or chemically converted, also be relatively mild, i.e.,not appreciably affecting or damaging the polymer backbone.

In a preferred embodiment of the present invention, when the radicallytransferable group is a halogen, the halogen can be removed by means ofa mild dehalogenation reaction. The reaction is typically performed as apost-reaction after the precursor polymer has been formed, i.e., priorto conversion of the precursor polymer to the polycarboxylic acidfunctional polymer, and in the presence of at least an ATRP catalyst.Preferably, the dehalogenation post-reaction is performed in thepresence of both an ATRP catalyst and its associated ligand.

The mild dehalogenation reaction is performed by contacting the halogenterminated precursor of the carboxylic acid functional polymer of thepresent invention that is substantially free of carboxylic acidfunctionality with one or more ethylenically unsaturated compounds,which are not readily radically polymerizable under at least a portionof the spectrum of conditions under which atom transfer radicalpolymerizations are performed, hereinafter referred to as “limitedradically polymerizable ethylenically unsaturated compounds” (LRPEUcompound(s)). As used herein, by “halogen terminated” and similar termsis meant to be inclusive also of pendent halogens, e.g., as would bepresent in branched, comb and star polymers.

Not intending to be bound by any theory, it is believed, based on theevidence at hand, that the reaction between the halogen terminatedprecursor polymer and one or more LRPEU compounds results in (1) removalof the terminal halogen group, and (2) the addition of at least onecarbon-carbon double bond where the terminal carbon-halogen bond isbroken. The dehalogenation reaction is typically conducted at atemperature in the range of 0° C. to 200° C., e.g., from 0° C. to 160°C., a pressure in the range of 0.1 to 100 atmospheres, e.g., from 0.1 to50 atmospheres. The reaction is also typically performed in less than 24hours, e.g., between 1 and 8 hours. While the LRPEU compound may beadded in less than a stoichiometric amount, it is preferably added in atleast a stoichiometric amount relative to the moles of terminal halogenpresent in the precursor polymer. When added in excess of astoichiometric amount, the LRPEU compound is typically present in anamount of no greater than 5 mole percent, e.g., 1 to 3 mole percent, inexcess of the total moles of terminal halogen.

Limited radically polymerizable ethylenically unsaturated compoundsuseful for dehalogenating the precursor polymer of the carboxylic acidfunctional polymer of the composition of toe present invention, undermild conditions, include those represented by the following generalformula XI.

In general formula XI, R₁ and R₂ can be the same or different organicgroups such as: alkyl groups having from 1 to 4 carbon atoms; arylgroups; alkoxy groups; ester groups; alkyl sulfur groups; acyloxygroups; and nitrogen-containing alkyl groups where at least one of theR₁ and R₂ groups is an organo group while the other can be an organogroup or hydrogen. For instance when one of R₁ or R₂ is an alkyl group,the other can be an alkyl, aryl, acyloxy, alkoxy, arenes,sulfur-containing alkyl group, or nitrogen-containing alkyl and/ornitrogen-containing aryl groups. The R₃ groups can be the same ordifferent groups selected from hydrogen or lower alkyl selected suchthat the reaction between the terminal halogen of the polymer and theLRPEU compound is not prevented. Also an R₃ group can be joined to theR₁ and/or the R₂ groups to form a cyclic compound.

It is preferred that the LRPEU compound be free of halogen groups.Examples of suitable LRPEU compounds include, but are not limited to,1,1-dimethylethylene, 1,1-diphenylethylene, isopropenyl acetate,alpha-methyl styrene, 1,1-dialkoxy olefin and mixtures thereof.Additional examples include dimethyl itaconate and diisobutene(2,4,4-trimethyl-l-pentene).

For purposes of illustration, the reaction between halogen terminatedprecursor polymer and LRPEU compound, e.g., alpha-methyl styrene, issummarized in the following general scheme 1

In general scheme 1, P-X represents the halogen terminated precursorpolymer, which is later converted to the polycarboxylic acid functionalpolymer of the composition of the present invention, as describedpreviously herein.

For each of general polymer structures IX and X, the subscripts r and seach independently have a value of 0 or more. Subscripts r and s eachindependently have a value of typically less than 100, preferably lessthan 50, and more preferably less than 10, for each of general polymerstructures IX and X. The values of r and s may each range between anycombination of these values, inclusive of the recited values.

The carboxylic acid functional polymer typically has a carboxylic acidequivalent weight of at least 100 grams/equivalent, and preferably atleast 200 grams/equivalent. The carboxylic acid equivalent weight of thepolymer is also typically less than 10,000 grams/equivalent, preferablyless than 5,000 grams/equivalent, and more preferably less than 1,000grams/equivalent. The carboxylic acid equivalent weight of thecarboxylic acid functional polymer may range between any combination ofthese values, inclusive of the recited values.

The number average molecular weight (Mn) of the carboxylic acidfunctional polymer is typically at least 250, more typically at least500, preferably at least 1,000, and more preferably at least 2,000. Thecarboxylic acid functional polymer also typically has a Mn of less than16,000, preferably less than 10,000, and more preferably less than5,000. The Mn of the carboxylic acid functional polymer may rangebetween any combination of these values, inclusive of the recitedvalues.

The carboxylic acid functional polymer may be used in the thermosettingcomposition of the present invention as a resinous binder or as anadditive with a separate resinous binder, which may be prepared by ATRPor by conventional polymerization methods. When used as an additive, thecarboxylic acid functional polymer as described herein typically has lowfunctionality, e.g., it may be monofunctional, and a correspondinglyhigh equivalent weight.

The carboxylic acid functional polymer (a) is typically present in thethermosetting composition of the present invention in an amount of atleast 50 percent by weight, preferably at least 70 percent by weight,and more preferably at least 80 percent by weight, based on total weightof resin solids of the thermosetting composition. The thermosettingcomposition also typically contains carboxylic acid functional polymerpresent in an amount of less than 98 percent by weight, preferably lessthan 95 by weight, and more preferably less than 90 percent by weight,based on total weight of resin solids of the thermosetting composition.The carboxylic acid functional polymer may be present in thethermosetting composition of the present invention in an amount rangingbetween any combination of these values, inclusive of the recitedvalues.

The thermosetting composition of the present invention may optionallyfurther comprise a polycarboxylic acid functional polyester.Polycarboxylic acid functional polyesters useful in the composition ofthe present invention typically have an average of at least twocarboxylic acid groups per polyester molecule. Polyesters havingcarboxylic acid functionality may be prepared by art-recognized methods,which include reacting carboxylic acids (or their anhydrides) havingacid functionalities of at least 2, and polyols having hydroxyfunctionalities of at least 2. As is known to those of ordinary skill inthe art, the molar equivalents ratio of carboxylic acid groups tohydroxy groups of the reactants is selected such that the resultingpolyester has carboxylic acid functionality and the desired molecularweight.

Examples of multifunctional carboxylic acids useful in preparing thepolycarboxylic acid functional polyester include, but are not limitedto, benzene-1,2,4-tricarboxylic acid, phthalic acid, tetrahydrophthalicacid, hexahydrophthalic acid,endobicyclo-2,2,1,5-heptyne-2,3-dicarboxylic acid, tetrachlorophthalicacid, cyclohexanedioic acid, succinic acid, isophthalic acid,terephthalic acid, azelaic acid, maleic acid, trimesic acid,3,6-dichlorophthalic acid, adipic acid, sebacic acid, and likemultifunctional carboxylic acids. Examples of polyols useful inpreparing the polycarboxylic acid functional polyester include, but arenot limited to, glycerin, trimethylolpropane, trimethylolethane,trishydroxyethylisocyanurate, pentaerythritol, ethylene glycol,propylene glycol, trimethylene glycol, 1,3-, 1,2- and 1,4-butanediols,heptanediol, hexanediol, octanediol, 2,2-bis(4-cyclohexanol)propane,neopentyl glycol, 2,2,3-trimethylpentane-1,3-diol,1,4-dimethylolcyclohexane, 2,2,4-trimethylpentane diol, and likepolyols.

Polycarboxylic acid functional polyesters useful in the presentinvention typically have an Mn within the range of from 1,000 to 10,000,e.g., from 2,000 to 7,000. The acid equivalent weight of the carboxylicacid functional polyester is typically within the range of from 290grams/equivalent to 3,000 grams / equivalent, e.g., from 500 to 2,000grams/equivalent. When present in the thermosetting composition of thepresent invention, the polycarboxylic acid functional polyester istypically present in an amount of from 1 percent to 40 percent byweight, based on the total weight of resin solids, e.g., from 5 percentto 35 percent by weight, based on the total weight of resin solids.

The thermosetting composition comprises also one or more epoxidefunctional crosslinking agents having at least two epoxide groups. Theepoxide functional crosslinking agent (b) is not prepared by ATRPmethods, and is preferably solid at room temperature. Classes of epoxidefunctional crosslinking agents useful in the composition of the presentinvention include, but are not limited to, epoxide functionalpolyesters, epoxide functional polymers prepared by conventional freeradical polymerization methods, epoxide functional polyethers, epoxidefunctional isocyanurates and mixtures thereof.

Epoxide functional polyesters useful in the present invention may beprepared by art-recognized methods. For example, the hydroxyl groups ofa hydroxy functional polyester may be reacted with 1-halo-2,3-epoxypropane, e.g., epichlorohydrin, to form the epoxide functionalpolyester. Polyesters having hydroxy functionality may be prepared bytraditional methods, which include reacting polyols having hydroxyfunctionalities of at least 2, and carboxylic acids (or theiranhydrides) having acid functionalities of at least 2. As is known tothose of ordinary skill in the art, the molar equivalents ratio ofhydroxy groups to carboxylic acid groups of the reactants is selectedsuch that the resulting polyester has hydroxy functionality and thedesired molecular weight. Examples of multifunctional carboxylic acidsand polyols useful in preparing the hydroxy functional polyesterprecursor of the epoxide functional polyester include, but are notlimited to, those recited previously herein with regard to the optionalpolycarboxylic acid functional polyester.

The Mn of epoxide functional polyesters useful in the present inventionis typically within the range of 1,000 to 10,000, e.g., from 2,000 to7,000. The equivalent weight of the epoxide functional polyester istypically within the range of 290 to 3,000 grams/equivalent, e.g., 500to 2,000 grams/equivalent.

Epoxide functional polymers prepared by conventional free radicalpolymerization methods that may be used as the epoxide functionalcrosslinking agent in the composition of the present invention are notprepared by ATRP. These epoxide functional polymer crosslinking agentsare typically prepared by copolymerizing epoxide functionalethylenically unsaturated radically polymerizable monomer(s), typicallya glycidyl functional (meth)acrylate, such as glycidyl (meth)acrylate,with ethylenically unsaturated radically polymerizable monomer(s) freeof epoxide functionality, e.g., alkyl (meth)acrylates. Typically, theepoxice functional polymer prepared by conventional free radicalpolymerization methods is an epoxide functional acrylic polymer.

The conventional radical polymerization methods by which the epoxidefunctional polymer crosslinking agent is prepared typically involve theuse of free radical initiators, such as organic peroxides and azo typecompounds. Optionally, chain transfer agents may also be used, e.g.,alpha-methyl styrene dimer and tertiary dodecyl mercaptan.

Examples of ethylenically unsaturated radically polymerizable monomersthat may be used in the preparation of the epoxide functional polymercrosslinking agent include, but are not limited to, glycidyl(meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate,2-(3,4-epoxycyclohexyl)ethyl (meth)acrylate and allyl glycidyl ether.Ethylenically unsaturated radically polymerizable monomer(s) free ofepoxide functionality that may be used to prepare the epoxide functionalpolymer crosslinking agent include those recited previously herein withregard to the M and G residues of the polycarboxylic acid functionalpolymer prepared by ATRP.

The Mn of the epoxide functional polymer crosslinking agent prepared byconventional free radical polymerization methods is typically less than10,000, e.g., between 1,000 and 5,000, and preferably between 1,000 and2,500. The epoxide functional polymer crosslinking agent usuallycontains from 3 to 6 moles of epoxide functional ethylenicallyunsaturated monomer per kilogram of epoxide functional polymercrosslinking agent, e.g., between 3.1 and 5.1 moles of epoxidefunctional monomer per kilograms of epoxide functional polymercrosslinking agent.

Epoxide functional polyether crosslinking agents useful in the presentinvention may be prepared by art-recognized methods. For example,polyols having two or more hydroxy groups and polyepoxides having two ormore epoxide groups are reacted in proportions such that the resultingpolyether has epoxide functionality, as is known to those of ordinaryskill in the art. The polyols and polyepoxides used in the preparationof the epoxide functional polyether may be selected from, for example,aliphatic, cycloaliphatic and aromatic polyols and polyepoxides, andmixtures thereof. Specific examples of polyols include those recitedpreviously herein. Polyepoxides useful in preparing the epoxidefunctional polyether include those resulting from the reaction of apolyol and epichlorohydrin, as is known to those skilled in the art. Ina preferred embodiment of the present invention, the epoxide functionalpolyether is prepared from 4,4′-isopropylidenediphenol and thediglycidyl ether of 4,4′-isopropylidenediphenol. An example of acommercially available epoxide functional polyether useful in thepresent invention is EPON® Resin 2002 from Shell Chemical Company.

The epoxide functional polyether crosslinking agent typically has a Mnof less than 10,000, e.g., between 1,000 and 7,000. The epoxideequivalent weight of the epoxide functional polyether crosslinking agentis typically less than 2,000 grams / equivalent, e.g., between 300 and1,000 grams/equivalent.

Epoxide functional isocyanurates are known and may be prepared byart-recognized methods. A preferred epoxide functional isocyanurate istris(2,3-epoxypropyl) isocyanurate.

The epoxide functional crosslinking agent (b) is typically present inthe thermosetting composition of the present invention in an amount ofat least 2 percent by weight, preferably at least 5 percent by weight,and more preferably at least 10 percent by weight, based on total weightof resin solids of the thermosetting composition. The thermosettingcomposition also typically contains epoxide functional crosslinkingagent present In an amount of less than 50 percent by weight, preferablyLess than 30 by weight, and more preferably less than 20 percent byweight, based on total weight of resin solids of the thermosettingcomposition. The epoxide functional crosslinking agent may be present inthe thermosetting composition of the present invention in an amountranging between any combination of these values, inclusive of therecited values.

To achieve a suitable level of cure with the thermosetting compositionof the present invention, the equivalent ratio of carboxylic acidequivalents is the polycarboxylic acid functional polymer (a) to epoxideequivalents in the epoxide functional crosslinking agent (b) istypically from 0.7:1 to 2:1, e.g., from 0.8:1 to 1.3:1. The aboverecited ranges of ratios are meant to also be inclusive of thecarboxylic acid equivalents associated with any polycarboxylic acidfunctional polyester(s) that may optionally be present in thecomposition.

The thermosetting composition of the present invention may also includepigments and fillers. Examples of pigments include, but are not limitedto, inorganic pigments, e.g., titanium dioxide and iron oxides, organicpigments, e.g., phthalocyanines, anthraquinones, quinacridones andthioindigos, and carbon blacks. Examples of fillers include, but are notlimited to, silica, e.g., precipitated silicas, clay, and bariumsulfate. When used in the composition of the present invention, pigmentsand fillers are typically present in amounts of from 0.1 percent to 70percent by weight, based on the total weight of the thermosettingcomposition.

The thermosetting composition of the present invention may optionallycontain additives such as waxes for flow and wetting, flow controlagents, e.g., poly(2-ethylhexyl)acrylate, degassing additives such asbenzoin, adjuvant resin to modify and optimize coating properties,antioxidants and ultraviolet (UV) light absorbers. Examples of usefulantioxidants and UV light absorbers include those available commerciallyfrom Ciba-Geigy under the trademarks IRGANOX and TINUVIN. These optionaladditives, when used, are typically present in amounts up to 20 percentby weight, based on total weight of the thermosetting composition.

The thermosetting composition of the present invention is typicallyprepared by first dry blending the carboxylic acid functional polymer,the epoxide functional crosslinking agent and additives, such as flowcontrol agents, decassing agents, antioxidants and UV absorbing agents,in a blender, e.g., a Henshel blade blender. The blender is operated fora period of time sufficient to result in a homogenous dry blend of thematerials charged thereto. The homogenous dry blend is then melt blendedin an extruder, e.g., a twin screw co-rotating extruder, operated withina temperature range of 80° C. to 140° C., e.g., from 100° C. to 125° C.The extrudate of the thermosetting composition of the present inventionis cooled and, when used as a powder coating composition, is typicallymilled to an average particle size of from, for example, 15 to microns.

In accordance with the present invention there is also provided, amethod of coating a substrate comprising:

(a) applying to said substrate a thermosetting composition;

(b) coalescing said thermosetting composition to form a substantiallycontinuous film; and

(c) curing said thermosetting composition by the application of heat,wherein said thermosetting composition comprises a co-reactable solid,particulate mixture as previously described herein.

The thermosetting composition of the present invention may be applied tothe substrate by any appropriate means that are known to those ofordinary skill in the art. Generally, the thermosetting composition isin the form of a dry powder and is applied by spray application.Alternatively, the powder can be slurried in a liquid medium such aswater, and spray applied. Where the language “co-reactable solid,particulate mixture” is used in the specification and claims, thethermosetting composition can be in dry powder form or in the form of aslurry.

When the substrate is electrically conductive, the thermosettingcomposition is typically electrostatically applied. Electrostatic sprayapplication generally involves drawing the thermosetting compositionfrom a fluidized bed and propelling it through a corona field. Theparticles of the thermosetting composition become charged as they passthrough the corona field and are attracted to and deposited upon theelectrically conductive substrate, which is grounded. As the chargedparticles begin to build up, the substrate becomes insulated, thuslimiting further particle deposition. This insulating phenomenontypically limits the film build of the deposited composition to amaximum of 3 to 6 mils (75 to 150 microns).

Alternatively, when the substrate is not electrically conductive, forexample as is the case with many plastic substrates, the substrate istypically preheated prior to application of the thermosettingcomposition. The preheated temperature of the substrate is equal to orgreater than that of the melting point of the thermosetting composition,but less than its cure temperature. With spray application overpreheated substrates, film builds of the thermosetting composition inexcess of 6 mils (150 microns) can be achieved, e.g., 10 to 20 mils (254to 508 microns). Substrates that may be coated by the method of thepresent invention include, for example, ferrous substrates, aluminumsubstrates, plastic substrates, e.g., sheet molding compound basedplastics, and wood.

After application to the substrate, the thermosetting composition isthen coalesced to form a substantially continuous film. Coalescing ofthe applied composition is generally achieved through the application ofheat at a temperature equal to or greater than that of the melting pointof the composition, but less than its cure temperature. In the case ofpreheated substrates, the application and coalescing steps can beachieved in essentially one step.

The coalesced thermosetting composition is next cured by the applicationof heat. As used herein and in the claims, by “cured” is meant a threedimensional crosslink network formed by covalent bond formation, e.g.,between the epoxide groups of the crosslinking agent and the carboxylicacid groups of the polymer. The temperature at which the thermosettingcomposition of the present invention is cured is variable and depends inpart on the amount of time during which curing is conducted. Typically,the thermosetting composition is cured at a temperature within the rangeof 149° C. to 204° C., e.g., from 154° C. to 177° C., for a period of 20to 60 minutes.

In accordance with the present invention there is further provided, amulti-component composite coating composition comprising:

(a) a base coat deposited from a pigmented film-forming composition; and

(b) a transparent top coat applied over said base coat, wherein saidtransparent top coat is deposited from a clear film-formingthermosetting composition comprising a co-reactable solid, particulatemixture as previously described herein. The multi-component compositecoating composition as described herein is commonly referred to as acolor-plus-clear coating composition.

The pigmented film-forming composition from which the base coat isdeposited can be any of the compositions useful in coatingsapplications, particularly automotive applications in whichcolor-plus-clear coating compositions are extensively used. Pigmentedfilm-forming compositions conventionally comprise a resinous binder anda pigment to act as a colorant. Particularly useful resinous binders areacrylic polymers, polyesters including alkyds, and polyurethanes.

The resinous binders for the pigmented film-forming base coatcomposition can be organic solvent-based materials such as thosedescribed in U.S. Pat. No. 4,220,679, note column 2 line 24 throughcolumn 4, line 40. Also, water-based coating compositions such as thosedescribed in U.S. Pat. Nos. 4,403,003, 4,147,679 and 5,071,904 can beused as the binder in the pigmented film-forming composition.

The pigmented film-forming base coat composition is colored and may alsocontain metallic pigments. Examples of suitable pigments can be found inU.S. Pat. Nos. 4,220,679, 4,403,003, 4,147,679 and 5,071,904.

Ingredients that may be optionally present in the pigmented film-formingbase coat composition are those which are well known in the art offormulating surface coatings and include surfactants, flow controlagents, thixotropic agents, fillers, anti-gassing agents, organicco-solvents, catalysts, and other customary auxiliaries. Examples ofthese optional materials and suitable amounts are described in theaforementioned U.S. Pat. Nos. 4,220,679, 4,403,003, 4,147,769 and5,071,904.

The pigmented film-forming base coat composition can be applied to thesubstrate by any of the conventional coating techniques such asbrushing, spraying, dipping or flowing, but are most often applied byspraying. The usual spray techniques and equipment for air spraying,airless spray and electrostatic spraying employing either manual orautomatic methods can be used. The pigmented film-forming composition isapplied in an amount sufficient to provide a base coat having a filmthickness typically of 0.1 to 5 mils (2.5 to 125 microns) and preferably0.1 to 2 mils (2.5 to 50 microns).

After deposition of the pigmented film-forming base coat composition onto the substrate, and prior to application of the transparent top coat,the base coat can be cured or alternatively dried. In drying thedeposited base coat, organic solvent and/or water, is driven out of thebase coat film by heating or the passage of air over its surface.Suitable drying conditions will depend on the particular base coatcomposition used and on the ambient humidity in the case of certainwater-based compositions. In general, drying of the deposited base coatis performed over a period of from 1 to 15 minutes and at a temperatureof 21° C. to 93° C.

The transparent top coat is applied over the deposited base coat by anyof the methods by which powder coatings are known to be applied.Preferably the transparent top coat is applied by electrostatic sprayapplication, as described previously herein. When the transparent topcoat is applied over a deposited base coat that has been dried, the twocoatings can be co-cured to form the multi-component composite coatingcomposition of the present invention. Both the base coat and top coatare heated together to conjointly cure the two layers. Typically, curingconditions of 149° C. to 204° C. for a period of 20 to 30 minutes areemployed. The transparent top coat typically has a thickness within therange of 0.5 to 6 mils (13 to 150 microns), e.g., from 1 to 3 mils (25to 75 microns).

The present invention is more particularly described in the followingexamples, which are intended to be illustrative only, since numerousmodifications and variations therein will be apparent to those skilledin the art. Unless otherwise specified, all parts and percentages are byweight.

SYNTHESIS EXAMPLES A AND B

Synthesis Examples A and B describe the preparation of carboxylic acidfunctional acrylic polymers that are used in the powder coatingcompositions of Examples 1 and 2. The carboxylic acid functional polymerof Example A is a comparative polymer prepared by non-living radicalpolymerization. The carboxylic acid functional polymer of Example B isrepresentative of a polymer useful in the thermosetting coatingcompositions of the present invention. The physical properties of thepolymers of Examples A and B are summarized in Table 1.

In synthesis Examples A and B, the following monomer abbreviations areused: methyl methacrylate (MhA); n-butyl methacrylate (n-BMA);tertiary-butyl methacrylate (t-BMA); and methacrylic acid (MAA).

EXAMPLE A

A comparative carboxylic acid functional polymer was prepared bystandard, i.e., non-controlled or non-living, radical polymerizationfrom the ingredients enumerated in Table A.

TABLE A Ingredients Parts by weight Charge 1 toluene 350 initiator (a)40 Charge 2 MMA 100 n-BMA 350 MAA 50 (a) 2,2′-azobis(2-methylbutanenitrile) initiator, obtained commercially from E.I. duPont de Nemours # and Company.

Charge 1 was heated to reflux temperature (at about 115° C.) atatmospheric pressure under a nitrogen blanket in a 2 liter round bottomflask equipped with a rotary blade agitator, reflux condenser,thermometer and heating mantle coupled together in a feed-back loopthrough a temperature controller, nitrogen inlet port, and two additionports. After holding Charge 1 for 30 minutes at reflux, Charge 2 wasadded over a period of 1 hour. With the completion of the addition ofCharge 2, the contents of the flask were held at reflux for anadditional 3 hours. The contents of the flask were then vacuum stripped.While still molten, the stripped contents of the flask were transferredto a suitable shallow open container and allowed to cool to roomtemperature and harden. The solidified resin was then broken intosmaller pieces, which were transferred to a suitable closed containerfor storage.

EXAMPLE B

A carboxylic acid functional polymer useful in the thermosettingcompositions of the present invention was prepared by atom transferradical polymerization from the ingredients listed in Table B.

TABLE B Ingredients Parts by weight toluene 350 copper (II) bromide (b)2.0 copper powder (c) 2.2 2,2′-bypyridyl 7.4diethyl-2-bromo-2-methylmalonate 50.6 MMA 100 n-BMA 350 t-BMA 83 (b) Thecopper (II) bromide was in the form of flakes and was obtained fromAldrich Chemical Company. (c) The copper powder had an average particlesize of 25 microns, a density of 1 gram/cm³, and was # obtainedcommercially from OMG Americas.

The ingredients were all added to a 2 liter 4-necked flask equipped witha motor driven stainless steel stir blade, water cooled condenser, and aheating mantle and thermometer connected through a temperature feed-backcontrol device. The contents of the flask were heated to and held at 85°C. for 4 hours. The contents of the flask were then cooled, filtered andthe solvent was removed by means of vacuum stripping. To the strippedresin was added 350 ml of dioxane, and a 3 times molar excess (relativeto the moles of t-EMA) of HCl (1 Molar in water). The resin, dioxane,HCl and water mixture was refluxed in a suitable round bottom flask for4 hours. The contents of the flask were then cooled to room temperatureand the pH was neutralized by the addition of sodium carbonate. Theneutralized contents of the flask were filtered, and the water anddioxane were removed by vacuum distillation in a suitable flask. Whilestill molten, the stripped contents of the flask were transferred to asuitable shallow open container and allowed to cool to room temperatureand harden. The solidified resin was then broken into smaller pieces,which were transferred to a suitable closed container for storage.

TABLE 1 Physical Data of the Polymers of Synthesis Examples A and BExample A Example B Mn (d) 3100 2840 Mw (d) 6045 3550 PDI (e) 1.95 1.25Tg onset (° C.) (f) 28.3 39.9 Tg midpoint (° C.) (f) 45.4 54.8 Tgendpoint (° C.) (f) 62.3 69.6 Melt Viscosity 572 112 at 180° C. (poise)(g) Acid Equivalent 896 925 Weight (h) Percent Weight Solids 99.8 99.9(i) (d) The molecular weight data was obtained by means of gelpermeation chromatography using # polystyrene standards. Theabbreviations are summarized as follows: number average molecular #weight (Mn); and weight average molecular weight (Mw). (e)Polydispersity index (PDI) = (Mw/Mn) (f) Glass transition temperature(Tg) onset, midpoint and endpoint values were determined by # means ofdifferential scanning calorimetry (DSC). The polymer samples underwent astress release # cycle followed by heating at a rate of 10° C./minute.(g) Melt viscosity at 180° C. was determined using a Brookfield CAP 2000High Temperature Viscometer. (h) Acid equivalent weight was determinedby titration with potassium hydroxide, and is shown in units of # gramsof resin / equivalent of acid. (i) Percent weight solids, based on totalweight was determined from 0.2 gram samples at 110° C. / 1 hour.

POWDER COATING COMPOSITION EXAMPLES 1AND 2

Powder coating Example 2 is representative of a thermosetting coatingcomposition according to the present invention, while powder coatingExample 1 is a comparative thermosetting coating composition example.The powder coating compositions were prepared from the ingredientsenumerated in Table 2.

TABLE 2 Powder Coating Compositions Ingredient Example 1 Example 2Polymer of 9 0 Example A Polymer of 0 9 Example Btriglycidylisocyanurate 1 1 crosslinker (j) Flow Controi Agent (k) 0.30.3 Benzoin 0.1 0.1 (j) triglycidylisocyanurate (TGIC) crosslinker,commercially availabie from ACETO Agricultural Chemical Corporation. (k)TROY 570 flow control agent, commercially available from TroyCorporation.

The ingredients listed in Table 2 were melt mixed by hand using aspatula on a hot plate at a temperature of 175° C. (347° F.). Themelt-mixed compositions were then coarsely ground by hand using a mortarand pestle. The course particulate thermosetting coating compositions ofExamples 1 and 2 were found to have 175° C. (347° F.) melt viscositiesof 36 poise and 23 poise respectively. The melt viscosities weredetermined using a temperature controlled cone and plate viscometermanufactured by Research Equipment (London) Ltd. These results show thata thermosetting coating composition according to the present invention,i.e., Example 2, has a lower melt viscosity than that of a comparativethermosetting coating composition, i.e., Example 1.

The present invention has been described with reference to specificdetails of particular embodiments thereof. It is not intended that suchdetails be regarded as limitations upon the scope of the inventionexcept insofar as and to the extent that they are included in theaccompanying claims.

We claim:
 1. A thermosetting composition comprising a co-reactablesolid, particulate mixture of: (a) a polycarboxylic acid functionalpolymer prepared by atom transfer radical polymerization initiated inthe presence of an initiator having at least one radically transferablegroup, and in which said polymer contains at least one of the followingpolymer chain structures: —[—(M)_(p)—(G)_(q)—]_(x)— and—[—(G)_(q)—(M)_(p)—]_(x)— wherein M is a residue, that is free ofcarboxylic acid functionality, of at least one ethylenically unsaturatedradically polymerizable monomer; G is a residue, that has carboxylicacid functionality, of at least one ethylenically unsaturated radicallypolymerizable monomer; p and q represent average numbers of residuesoccurring in a block of residues in each polymer chain structure; and p,q and x are each individually selected for each structure such that saidpolycarboxylic acid functional polymer has a number average molecularweight of at least 250 and polydispersity index of less than 2.5; and(b) epoxide functional crosslinking agent having at least two epoxidegroups.
 2. The composition of claim 1 wherein said polycarboxylic acidfunctional polymer is selected from the group consisting of linearpolymers, branched polymers, hyperbranched polymers, star polymers,graft polymers and mixtures thereof.
 3. The composition of claim 1wherein said polycarboxylic acid functional polymer has a number averagemolecular weight of from 500 to 16,000, and a polydispersity index ofless than 2.0.
 4. The composition of claim 1 wherein said initiator isselected from the group consisting of linear or branched aliphaticcompounds, cycloaliphatic compounds, aromatic compounds, polycyclicaromatic compounds, heterocyclic compounds, sulfonyl compounds, sulfenylcompounds, esters of carboxylic acids, polymeric compounds and mixturesthereof, each having at least one radically transferable halide.
 5. Thecomposition of claim 4 wherein said initiator is selected from the groupconsisting of halomethane, methylenedihalide, haloform, carbontetrahalide, 1-halo-2,3-epoxypropane, p-methanesulfonyl halide,p-toluenesulfonyl halide, methanesulfenyl halide, p-toluenesulfenylhalide, 1-phenylethyl halide, C₁-C₆-alkyl ester of2-halo-C₁-C₆-carboxylic acid, p-halomethylstyrene,mono-hexakis(α-halo-C₁-C₆-alkyl)benzene, diethyl-2-halo-2-methylmalonate, ethyl 2 -bromoisobutyrate and mixtures thereof.
 6. Thecomposition of claim 1 wherein said polycarboxylic acid functionalpolymer has a carboxylic acid equivalent weight of from 100 to 10,000grams/equivalent.
 7. The composition of claim 1 wherein M is derivedfrom at least one of vinyl monomers, allylic monomers and olefins. 8.The composition of claim 7 wherein M is derived from at least one ofalkyl (meth)acrylates having from 1 to 20 carbon atoms in the alkylgroup, vinyl aromatic monomers, vinyl halides, vinyl esters ofcarboxylic acids and olefins.
 9. The composition of claim 1 wherein saidepoxide functional crosslinking agent (b) is selected from the groupconsisting of epoxide functional polyesters, epoxide functional polymersprepared by free radical polymerization methods, epoxide functionalpolyethers, epoxide functional isocyanurates and mixtures thereof. 10.The composition of claim 9 wherein said epoxide functional crosslinkingagent (b) is tris(2,3-epoxypropyl)isocyanurate.
 11. The composition ofclaim 1 wherein the equivalent ratio of carboxylic acid equivalents insaid polycarboxylic acid functional polymer (a) to epoxy equivalents insaid epoxide functional crosslinking agent (b) is within the range of0.7:1 to 2:1.
 12. The composition of claim 1 wherein said polycarboxylicacid functional polymer (a) is present in said thermosetting compositionin an amount of from 50 to 98 percent by weight, based on total resinsolids weight, and said epoxide functional crosslinking agent (b) ispresent in said thermosetting composition in an amount of from 2 to 50percent by weight, based on total resin solids weight.
 13. Thecomposition of claim 1 wherein G is derived from: alkyl (meth)acrylate,which after polymerization is hydrolyzed; or at least one hydroxyfunctional ethylenically unsaturated radically polymerizable monomer,which after polymerization is post-reacted with a cyclic anhydride. 14.The composition of claim 13 wherein G is derived from: C₁-C₄ alkyl(meth)acrylate, which after polymerization is hydrolyzed; or at leastone of hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate,which after polymerization is post-reacted with a cyclic anhydride. 15.The composition of claim 1 wherein said polycarboxylic acid functionalpolymer (a) has at least one of the following polymer chain structures:φ−[[(M)_(p)−(G)_(q)]_(x)−(M)_(r) −T]_(z) andφ−[[(G)_(q)−(M)_(p)]_(x)−(G)_(s) −T]_(z) wherein φ is or is derived fromthe residue of said initiator free of said radically transferable group;T is or is derived from said radically transferable group of saidinitiator; x is independently from 1 to 100 for each structure; p and qare each independently within the range of 0 to 100 for each x-segmentand for each structure, the sun of p and q being at least 1 for eachx-segment, and q being at least 1 for at least one x-segment; r and sare each independently for each structure within the range of 0 to 100;z is independently for each structure at least 1; and saidpolycarboxylic acid functional polymer has a polydispersity index ofless than 2.0.
 16. The composition of claim 15 wherein saidpolycarboxylic acid functional polymer has a number average molecularweight of from 500 to 16,000, and a polydispersity index of less than1.8.
 17. The composition of claim 15 wherein p is independently selectedfor each structure within the range of 1 to 20; and q is independentlyselected for each structure within in the range of 1 to
 20. 18. Thecomposition of claim 15 wherein x is independently selected for eachstructure within the range of 1 to
 50. 19. The composition of claim 15wherein T is halide.
 20. The composition of claim 19 wherein T isderived from a dehalogenation post-reaction.
 21. The composition ofclaim 20 wherein said dehalogenation post-reaction comprises contactinga precursor of said polycarboxylic acid functional polymer that issubstantially free of carboxylic acid functionality with a limitedradically polymerizable ethylenically unsaturated compound.
 22. Thecomposition of claim 21 wherein said limited radically polymerizableethylenically unsaturated compound is selected from the group consistingof 1,1-dimethylethylene, 1,1-diphenylethylene, isopropenyl acetate,alpha-methyl styrene, 1,1-dialkoxy olefin and combinations thereof. 23.The composition of claim 1 further comprising polycarboxylic acidfunctional polyester.
 24. The composition of claim 23 wherein saidpolycarboxylic acid functional polyester has a carboxylic acidequivalent weight of from 290 grams/equivalent to 3,000grams/equivalent, and is present in said composition in an amount offrom 1 percent by weight to 40 percent by weight, based on the totalweight of resin solids.